1. Field of Invention
This invention relates to the separation of different types of biological objects.
2. Prior Art
It is often desirable to examine biological samples, and specimens for signs of abnormality and disease. A partial list of biological samples is bodily fluids such as blood, urine, and spinal fluids, Tissue, and tumor biopsies, water and soil samples, and plant tissues and fluids. Current practice is to search for and examine the biological objects of interest in the sample. A partial list of biological objects is cells, bacteria, viruses, and yeast. Within the sample there are usually a large number of biological objects of the same that are not of interest. It is therefore advantageous to separate and remove most of objects that are not of interest thus concentrating the objects of interest.
As an example, the cells in a sample of blood or spinal fluid might need to be examined for indications of cancer. Because these types of samples might well contain millions of cells, it is very advantageous to separate the majority cells and fluids that are not of interest, thus concentrating the cells of interest.
In blood and spinal fluids it is desirable to remove plasma, erythrocytes red blood cells, and leukocytes (white blood cells), thus concentrating the small number of cells that are not normally present and that might exhibit signs of abnormality such as cancer. As leukocytes are often very similar to the cells of interest it is difficult to remove these cells without losses. The resulting concentrated cells of interest are then used for further analysis.
Prior to the invention the main methods of separating cell types were: Separation by size, by centrifugation (density/specific gravity), and chemical properties.
Separation by size is usually done by filtering through a filter, or a array of one or more hollow tubes with a specific hole size. Cells that are larger then the hole stay on one side of the filter while smaller cells go through the filter and are collected on the other side of the filter. If the two types of cells have an overlapping size distribution (a certain portion of the cells of one type are larger while another portion are smaller then the other type of cell), then the filter does not separate the two types effectively, resulting in a loss of some of the cells of interest thus reducing separation efficiency. Moreover, filtering using too high of a force can cause cells to rupture.
Separation by centrifugation works well when the two types of cells are very different as in the example of the separation of white and red blood cells. But centrifugation fails when the two types of cells have similar density and size, such as white blood cells and cancer cells. A further limitation of centrifugation-based cell separation is that the density of the cells are not constant, as even dead cells react to the conditions of their surrounding and environment.
Separation by chemical properties utilizing immuno-based chemistry by antibody binding of the cell to a surface antigen (which can possibly be attached to magnetic beads) is expensive, labor-intensive, and time-consuming. Many of the steps can have cell losses thus reducing the separation efficiency of this type of method. Also, cells will be lost if they don't have the matching antigen, and/or if the antigen is obscured by other blood components. Blood plasma proteins may coat the cells in circulation (a possible method of cancer cells evading the immune system) thus preventing their recognition by the antibody. The cells separated by this method are often in a form that is difficult for a visual examination of the results.
Separation by the above methods can damage the cells both bio-chemically, and mechanically, thus changing the cell morphology, and inhibiting subsequent processing, and analysis.